liballoc: introduce String, Vec const-slicing
This change `const`-qualifies many methods on `Vec` and `String`, notably `as_slice`, `as_str`, `len`. These changes are made behind the unstable feature flag `const_vec_string_slice`.
## Motivation
This is to support simultaneous variance over ownership and constness. I have an enum type that may contain either `String` or `&str`, and I want to produce a `&str` from it in a possibly-`const` context.
```rust
enum StrOrString<'s> {
Str(&'s str),
String(String),
}
impl<'s> StrOrString<'s> {
const fn as_str(&self) -> &str {
match self {
// In a const-context, I really only expect to see this variant, but I can't switch the implementation
// in some mode like #[cfg(const)] -- there has to be a single body
Self::Str(s) => s,
// so this is a problem, since it's not `const`
Self::String(s) => s.as_str(),
}
}
}
```
Currently `String` and `Vec` don't support this, but can without functional changes. Similar logic applies for `len`, `capacity`, `is_empty`.
## Changes
The essential thing enabling this change is that `Unique::as_ptr` is `const`. This lets us convert `RawVec::ptr` -> `Vec::as_ptr` -> `Vec::as_slice` -> `String::as_str`.
I had to move the `Deref` implementations into `as_{str,slice}` because `Deref` isn't `#[const_trait]`, but I would expect this change to be invisible up to inlining. I moved the `DerefMut` implementations as well for uniformity.
This change `const`-qualifies many methods on Vec and String, notably
`as_slice`, `as_str`, `len`. These changes are made behind the unstable
feature flag `const_vec_string_slice` with the following tracking issue:
https://github.com/rust-lang/rust/issues/129041
Rewrite these blobs to explicitly mention the case of a sized operand.
The previous made that seem wrong instead of emphasizing it is nothing
but a simple cast. Instead, the explanation now emphasizes that the
address portion of the argument, together with its provenance, is
discarded which previously had to be inferred by the reader. Then an
example demonstrates a simple line of incorrect usage based on this
idea of provenance.
Android: Debug assertion after setting thread name
While `prctl` cannot fail if it points to a valid buffer, it's still better to assert the result as it's done for other places.
make Cell unstably const
Now that we can do interior mutability in `const`, most of the Cell API can be `const fn`. :) The main exception is `set`, because it drops the old value. So from const context one has to use `replace`, which delegates the responsibility for dropping to the caller.
Tracking issue: https://github.com/rust-lang/rust/issues/131283
`as_array_of_cells` is itself still unstable to I added the const-ness to the feature gate for that function and not to `const_cell`, Cc #88248.
r? libs-api
std: replace `LazyBox` with `OnceBox`
This PR replaces the `LazyBox` wrapper used to allocate the pthread primitives with `OnceBox`, which has a more familiar API mirroring that of `OnceLock`. This cleans up the code in preparation for larger changes like #128184 (from which this PR was split) and allows some neat optimizations, like avoid an acquire-load of the allocation pointer in `Mutex::unlock`, where the initialization of the allocation must have already been observed.
Additionally, I've gotten rid of the TEEOS `Condvar` code, it's just a duplicate of the pthread one anyway and I didn't want to repeat myself.
Stabilize the `map`/`value` methods on `ControlFlow`
And fix the stability attribute on the `pub use` in `core::ops`.
libs-api in https://github.com/rust-lang/rust/issues/75744#issuecomment-2231214910 seemed reasonably happy with naming for these, so let's try for an FCP.
Summary:
```rust
impl<B, C> ControlFlow<B, C> {
pub fn break_value(self) -> Option<B>;
pub fn map_break<T>(self, f: impl FnOnce(B) -> T) -> ControlFlow<T, C>;
pub fn continue_value(self) -> Option<C>;
pub fn map_continue<T>(self, f: impl FnOnce(C) -> T) -> ControlFlow<B, T>;
}
```
Resolves#75744
``@rustbot`` label +needs-fcp +t-libs-api -t-libs
---
Aside, in case it keeps someone else from going down the same dead end: I looked at the `{break,continue}_value` methods and tried to make them `const` as part of this, but that's disallowed because of not having `const Drop`, so put it back to not even unstably-const.
what matters is we re doing the right things as doing sizeof, rather than
KINFO_FILE_SIZE (only defined on intel architectures), the kernel
making sure it matches the expectation in its side.
Avoid emptiness check in `PeekMut::pop`
This PR avoids an unnecessary emptiness check in `PeekMut::pop` by replacing `Option::unwrap` with `Option::unwrap_unchecked`.
Add `get_line` confusable to `Stdin::read_line()`
This pull request resolves https://github.com/rust-lang/rust/issues/131091
---
I've updated tests for `tests/ui/attributes/rustc_confusables_std_cases` in order to verify this change is working as intended.
Before I submitted this pull request, I had a pull request to my local fork. If you're interested in seeing the conversation on that PR, go to https://github.com/JakenHerman/rust/pull/1.
---
**Testing**:
Run `./x.py test tests/ui/attributes/rustc_confusables_std_cases.rs`
impl `Default` for `HashMap`/`HashSet` iterators that don't already have it
This is a follow-up to #128261 that isn't included in that PR because it depends on:
* [x] rust-lang/hashbrown#542 (`Default`)
* [x] `hashbrown` release containing above
It also wasn't included in #128261 initially and should have its own FCP, since these are also insta-stable.
Changes added:
* `Default for hash_map::{Iter, IterMut, IntoIter, IntoKeys, IntoValues, Keys, Values, ValuesMut}`
* `Default for hash_set::{Iter, IntoIter}`
Changes that were added before FCP, but are being deferred to later:
* `Clone for hash_map::{IntoIter, IntoKeys, IntoValues} where K: Clone, V: Clone`
* `Clone for hash_set::IntoIter where K: Clone`
std: make `thread::current` available in all `thread_local!` destructors
... and thereby allow the panic runtime to always print the right thread name.
This works by modifying the TLS destructor system to schedule a runtime cleanup function after all other TLS destructors registered by `std` have run. Unfortunately, this doesn't affect foreign TLS destructors, `thread::current` will still panic there.
Additionally, the thread ID returned by `current_id` will now always be available, even inside the global allocator, and will not change during the lifetime of one thread (this was previously the case with key-based TLS).
The mechanisms I added for this (`local_pointer` and `thread_cleanup`) will also allow finally fixing #111272 by moving the signal stack to a similar runtime-cleanup TLS variable.
Update hashbrown to 0.15 and adjust some methods
This PR updates `hashbrown` to 0.15 in the standard library and adjust some methods as well as removing some as they no longer exists in Hashbrown it-self.
- `HashMap::get_many_mut` change API to return array-of-Option
- `HashMap::{replace_entry, replace_key}` are removed, FCP close [already finished](https://github.com/rust-lang/rust/issues/44286#issuecomment-2293825619)
- `HashSet::get_or_insert_owned` is removed as it no longer exists in hashbrown
Closes https://github.com/rust-lang/rust/issues/44286
r? `@Amanieu`
